This page will take a closer look at the earth-antenna-space interface which affects loop propagation, and concerns us with earth conductivity, permittivity and permeability, which controls (or sets) the relative speed (and phase) of the ‘surface’ wave (also known as the ‘ground wave’ in radio/ham circles) in contrast to the ‘space’ wave which exists some distance above the earth (and out of the influence of the ‘surface’ of the earth.)
This earth-antenna-space interface is notably operative at lower frequencies where ‘ground wave’ action or propagation is seen to be strong, at frequencies say, below a couple (2) MHz, although ‘ground wave’ can exist at 3 or 4 MHz if ground conductivity is ‘good’ enough.
We shall now begin to look at different modes of radio wave propagation in/near mediums (as opposed to free space) with an emphasis on the longer wavelengths (where groundwave propagation is a usable propagation mode):
1) PROPAGATION OF LONG RADIO WAVES
The link above is a particularly good discussion on Long Wave propagation, and includes graphs and charts showing LW propagation attenuation over land and sea as shown in this example graph (click on image for full size):
An example of the ‘sloped wave front’ close to ground due to the non-ideal conductivity (loss) of real earth:
2) Surface Wave propagation
3) Surface waves; A a very practical example as seen in the Gaubau Line: